Proportion Calculator – Find Missing Variable (x)

The missing variable (x) from two ratios can be easily found using this proportion calculator solver. This tool will find the missing value if you only enter the three values.

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What is Proportion?

The phrases ratio and direct proportion are related yet frequently confused.

We refer to two ratios as being in direct proportion when they are the same. A photo that has been enlarged is a helpful visual aid for explaining direct proportion.

Two pictures are shown below. The larger image is 6 cm long and 4 cm wide, and the smaller image is 3 cm long and 2 cm wide. The following are their length to width ratios:

Small Image = Ratio of length/width = 3/2

Large Image = Ratio of length/width = 6/4 = 3/2 (dividing the numerator and denominator by 2)

Because the ratios of length to width for each photograph are equal, we say that the lengths and widths of the two images are in direct proportion.

We refer to two figures as being comparable if their ratios are identical. This suggests that if one figure is an enlargement of the other, then the two figures are similar.

How to Use Proportion Calculator?

  • As you can see, this calculator has 4 input boxes that stand for 2 ratios. Simply enter the three values into the corresponding fields, and the fourth value will be calculated for you

How to Solve Proportion Examples ?

We’ve covered a few examples below that demonstrate simple procedures for finding the missing variable (x)┬áin two proportions.


1. What is the value of x in 5 : 9 :: 15 : x?

Solution :

Finding the missing value (x) in these given proportions is very simple if you are familiar with cross multiplication.

First we will arrange the proportions in proper ratios,

5/9 =15/x

To find the value of “x,” just cross-multiply the numbers.

5*x = 15*9
5*x = 135
x = 135/5
x = 27

The value of x is 27.


2. On his bicycle, Roberts travels 5 miles in 25 minutes. If he doesn’t take any break, how long will it take him to travel 25 miles?

Solution :

Here the missing value (time) in the example is ‘x’. We will arrange the numbers in proper proportion so that we can find the missing value.

5 miles in 25 minutes then 25 miles in x-minutes.

5/25 = 25/x

Using cross-multiplication,

5*x = 25*25
5*x = 625
x = 625/5
x = 125

Robert will cover 25 miles on his bicycle in 125 minutes.


3. Solve for x – x:4 = 12:48


Arrange the equation in proper ratio

x/4 = 12/48

Cross multiply to find the value of x

x*48 = 12*4
x*48 = 48
x = 48/48
x = 1

The value of variable x is 1